This invention relates to a shift control apparatus for a continuously variable transmission.
In a continuously variable transmission for a vehicle, there are a belt type continuously variable transmission, a troidal continuously variable transmission, and so on. A speed ratio of any of the transmission is controlled in accordance with a running state of the vehicle.
For example, the belt type continuously variable transmission includes a primary pulley, a secondary pulley, and a belt wound around the primary pulley and the secondary pulley. The belt type continuously variable transmission transmits a rotational driving force (torque) inputted to the primary pulley, through the belt to the secondary pulley while a transmission gear ratio is continuously varied by varying radii of the primary and secondary pulleys around which the belt is wound.
A shift control apparatus of the continuously variable transmission includes a shift diagram set based on simulations, tests and so on, and performs a shift control based on a shift line defined in this shift diagram.
For example, in case of the belt type continuously variable transmission, a target rotational speed of the primary pulley is set from the shift diagram based on the accelerator opening degree and the vehicle speed. A target transmission gear ratio (pulley ratio) is set from this set target rotational speed. The shift control apparatus controls the primary pulley and the secondary pulley so that groove widths of the primary pulley and the secondary pulley become groove widths to attain the set transmission gear ratio.
A Japanese Patent Application Publication No. 2005-164000 discloses a shift control apparatus for a continuously variable transmission which is configured to judge whether or not the driver has an acceleration intention based on an accelerator operation of the driver, to switch from a normal shift line to a shift line for the acceleration when it is judged that the driver has the acceleration intention, and to set the target transmission gear ratio based on the transmission line for the acceleration.